The invention relates to a solid-state trip device for a multipole electrical circuit breaker protecting an A.C. electrical supply system comprising:
a current sensor per pole, which generates a signal proportional to the current flowing through the associated conductor of the supply system protected by the circuit breaker;
a detection and rectification circuit to which said signals are applied to supply on the one hand signals representative of the currents flowing through the conductors to be protected and on the other hand a zero sequence signal if an insulation fault occurs;
an electronic processing unit to which the output signals from the detection and rectification circuit are applied to perform delayed and/or instantaneous tripping functions and delivering, with or without a time delay, a circuit breaker tripping order when preset thresholds are exceeded by the signals representative of the currents flowing through the conductors or by the zero sequence signal.
In state-of-the-art solid-state trip devices, a current transformer is associated with each of the conductors of the supply system to be protected, the signal it delivers being applied to a full-wave rectifier bridge, the rectified signals being used by an electronic processing unit to perform the long delay, short delay and/or instantaneous trip device functions. A ground fault :s generally speaking detected either by means of an additional, summing, current transformer whose primary windings are constitute by the set of conductors of the supply system to be protected and whose secondary winding supplies a ground fault signal when the sum of the currents flowing through the primary windings is not nil, or by means of a measurement resistor arranged in a conductor common to one of the ends of each secondary winding of the current transformers associated with the different conductors.